(1) Field of the Invention
This invention relates to seals, and more particularly to metallic seals.
(2) Description of the Related Art
A variety of metallic seal configurations exist. Key metallic seals are commonly held under compression between two opposed flanges of the elements being sealed to each other. Such metallic seals may be used in a variety of industrial applications.
Key examples of such metallic seals are of an annular configuration, having a convoluted radial section which permits the seal to act as a spring and maintain engagement with the flanges despite changes or variations in the flange separation. Certain such seals have an S-like section while others have a section similar to the Greek letter Σ with diverging base and top portions. Other similar seals are formed with additional convolutions. One exemplary seal is sold by The Advanced Products Company, North Haven, Conn., as the E-RING seal. Such seals are commonly formed as a monolithic piece of stainless steel or superalloy. Such seals are commonly formed from sheet stock into a shape which is effective to provide the seal with a desired range of compressibility from a relaxed condition. These seals are installed in applications in a compressed state as shown in FIG. 1. The total compression (ΔhT) consists of an elastic component (ΔhEL) and plastic component (ΔhPL) so thatΔhT=ΔhEL+ΔhPL With continued exposure at elevated temperatures, the plastic component ΔhPL grows resulting from creep and the elastic component ΔhEL decreases with time. As a result, the sealing load or the capability of the seal to follow the flange movement also diminishes with time resulting from the reduced ΔhEL. This phenomenon is called stress relaxation.